Patent Ductus ArteriosusCongenital Heart Defect

Definition:Patent ductus arteriosus, or PDA, is

a heart condition that is normal but reverses soon after birth. In a persistent PDA, there is an irregular transmission of blood between two of the most important arteries in close proximity to the heart. Although the ductus arteriosus normally seals off within a few days, in PDA, the newborn's ductus arteriosus does not close but remains patent.

. PDA is common in neonates with persistent respiratory problems such as hypoxia, and has a high occurrence in premature children.

In hypoxic newborns, too little oxygen reaches the lungs to produce sufficient levels of bradykinin. Bradykinin is responsible for the vasodilation of blood vessels, in this case it is responsible for the patency of the ductus arteriosus.

Connection of the aorta with the pulmonary artery

Before birth, the two major arteries—the aorta and the pulmonary artery—are connected by a blood vessel called the ductus arteriosus. This vessel is an essential part of fetal blood circulation.

Causes:A patent ductus arteriosus can

be idiopathic (i.e. without an identifiable cause), or secondary to another condition.

Some common contributing factors in humans include:Premature infantsCongenital rubella syndromeChromosomal abnormalities such as

Down Syndrome

Another cause of PDA is when during the first several weeks after birth there is a decrease in the blood supply or oxygen saturation of the baby which could lead to the return of the fetal type circulation in the baby and induce the reopening of the ductus arteriosus.

Signs and Symptoms:tachycardia or other arrhythmiadifficulty breathing because the lungs are

wet, congested, or fluid-filled (congestive heart failure)

continuous machine-like murmurenlarged heartLeft subclavicular thrillBounding pulseWidened pulse pressureexcessive work load on heart that interferes

with breathing, feeding, or sleeping

Risk Factors:Experiencing any of the following conditions during

pregnancy can increase your risk of having a baby with a heart defect. Rubella infection. Becoming infected with rubella

(German measles) while pregnant can increase the risk of fetal heart defects. The rubella virus crosses the placenta and spreads through the fetus's circulatory system damaging blood vessels and organs, including the heart.

Poorly controlled diabetes. Uncontrolled diabetes in the mother in turn affects the fetus's blood sugar causing various damaging effects to the developing fetus.

Drug or alcohol use or exposure to certain substances. Use of certain medications, alcohol or drugs, or exposure to chemicals or radiation during pregnancy can harm the developing fetus.

Demographic Factors: Race/Ethnicity

◦ Studies of risk of PDA by race/ethnicity have been inconsistent. While some studies have reported higher rates of PDA among African Americans than among whites, other investigations found no such difference . PDA rates among Hispanics tend to be lower than among whites and African Americans (Fixler 1993, Chavez 1988).

Sex◦ PDA is more common among females than among males,

although one investigation reported 53% of the PDA cases to be among males (Lary 2001).

Parity◦ One study noted isolated PDA not to be associated with

the mother’s number of previous pregnancies. Another study reported PDA risk to decrease with increasing birth order (Rothman 1976).

Plurality◦ Several investigations reported increased risk of PDA among twins

while a more recent study found no association between isolated PDA risk and twins (Ferencz 1997).

Gestational Age and Birth Weight◦ As noted previously, PDA is associated with preterm delivery, where

PDA generally is not considered to be a birth defect. However, among term births isolated PDA risk is associated with lower birth weight. PDA risk is associated with small for gestational age (intrauterine growth retardation). One study indicated that there was an association between PDA and hypothyroidism in the newborn. The defect corrected itself after thyroid replacement therapy in most cases (Allegaert 2004).

Consanguinity◦ One investigation reported no increased risk of PDA among the

offspring born to first cousins. However, another study indicated that within an Iranian population with a high level of consanguinity the rates of PDA were higher than when compared to the United States population (15% vs. 2-7%) (Mani 2004).

Parental Age◦Several studies observed decreased

risk of PDA with increasing maternal age. However, another study noted no association between isolated PDA and maternal or paternal age (Ferencz 1997).

Pathophysiology:As a baby develops in the womb, a vascular

connection (ductus arteriosus) between two major blood vessels leading from the heart — the aorta and pulmonary artery — is a normal and necessary part of fetal circulation.

But, this duct is supposed to close within two or three days after birth once the newborn's heart adapts to life outside the womb.

In premature infants, the duct often closes on its own within a few weeks of birth.

But if the duct remains open, it's referred to as a patent ductus arteriosus.

Heart with PDA

Normal heart

Complications:Larger defects that are untreated can cause high

blood pressure in the lungs (pulmonary hypertension), frequent lung infections, irregular heartbeat (arrhythmia) or heart failure, a chronic condition in which the heart can't pump effectively.

People with structural heart problems, such as a patent ductus arteriosus, are at a higher risk of infectious endocarditis than is the general population. Infectious endocarditis is an inflammation of the inner lining of the heart caused by a bacterial infection.

Rarely, pulmonary hypertension can cause permanent lung damage, and pulmonary hypertension becomes irreversible (Eisenmenger's syndrome).

Treatment:Medications

n premature infants, an intravenous (IV) medication called indomethacin may help close a patent ductus arteriosus. Indomethacin is related to aspirin and ibuprofen and works by stimulating the muscles inside the PDA to constrict, thereby closing the connection. Your child's physician can answer any further questions you may have about this treatment.◦ digoxin - a medicine that helps strengthen the heart

muscle, enabling it to pump more efficiently.◦ diuretics - the body's water balance can be affected

when the heart is not working as well as it could. These medications help the kidneys remove excess fluid from the body.

Treatment: (surgical) An incision may be made

through the breastbone (sternum) and between the lungs (mediastinum) while the child is deep asleep and pain-free (under general anesthesia). For some heart defect repairs, the incision is made on the side of the chest, between the ribs (thoracotomy) instead of through the breastbone. Heart-lung bypass may be needed. Tubes are used to re-route the blood through a special pump that adds oxygen to the blood and keeps it warm and moving through the rest of the body while the repair is being done.

Treatment: (surgical) Most children need to stay

in the Intensive Care Unit for 3 to 7 days and stay in the hospital for 5 to 14 days. By the time the child is transferred out of the intensive care unit, most of the tubes and wires have been removed and he is encouraged to resume many of his daily activities. At the time of discharge, the parents are instructed on activity, how to care for the incision and how to give medications their child may need to take such as Digoxin, Lasix, Aldactone and Coumadin. The child needs at least several more weeks at home to recover.

Treatment: (conservative) Most infants with PDA eat and grow normally, but

premature infants or those infants with a large PDA may become tired when feeding, and are not able to eat enough to gain weight. Options that can be used to ensure your baby will have adequate nutrition include the following: ◦ high-calorie formula or breast milk

Special nutritional supplements may be added to formula or pumped breast milk that increase the number of calories in each ounce, thereby allowing your baby to drink less and still consume enough calories to grow properly.

◦ supplemental tube feedingsFeedings given through a small, flexible tube that passes through the nose, down the esophagus, and into the stomach, can either supplement or take the place of bottle-feedings. Infants who can drink part of their bottle, but not all, may be fed the remainder through the feeding tube. Infants who are too tired to bottle-feed may receive their formula or breast milk through the feeding tube alone.

Prevention: In most cases, you can't do anything to prevent having a

baby with a heart defect. However, it's important to do everything possible to have a healthy pregnancy. Here are the basics: ◦ Get early prenatal care, even before you're pregnant.

Quitting smoking, reducing stress, stopping birth control — these are all things to talk to your doctor about before you get pregnant. Also, be sure you talk to your doctor about any medications you're taking.

◦ Eat a well-balanced diet. Include a vitamin supplement that contains folic acid. Also, limit caffeine.

◦ Exercise regularly. Work with your doctor to develop an exercise plan that's right for you.

◦ Avoid risks. These include harmful substances such as alcohol, cigarettes and illicit drugs. Also, avoid X-rays, hot tubs and saunas.

◦ Avoid infections. Be sure you are up to date on all of your vaccinations before becoming pregnant. Certain types of infections can be harmful to a developing fetus.

Tetralogy of FallotCongenital Heart Defect

Definition:Tetralogy of Fallot (TOF) is a

congenital heart defect which is classically understood to involve four anatomical abnormalities (although only three of them are always present). It is the most common cyanotic heart defect, representing 55-70%, and the most common cause of blue baby syndrome.

Heart with TOF Normal heart

Primary four malformations:A: Pulmonary stenosis

◦ A narrowing of the right ventricular outflow tract and can occur at the pulmonary valve (valvular stenosis) or just below the pulmonary valve (infundibular stenosis). Infundibular pulmonic stenosis is mostly caused by overgrowth of the heart muscle wall (hypertrophy of the septoparietal trabeculae), however the events leading to the formation of the overriding aorta are also believed to be a cause. The pulmonic stenosis is the major cause of the malformations, with the other associated malformations acting as compensatory mechanisms to the pulmonic stenosis. The degree of stenosis varies between individuals with TOF, and is the primary determinant of symptoms and severity. This malformation is infrequently described as sub-pulmonary stenosis or subpulmonary obstruction.

Primary four malformations:B: Overriding aorta

◦An aortic valve with biventricular connection, that is, it is situated above the ventricular septal defect and connected to both the right and the left ventricle. The degree to which the aorta is attached to the right ventricle is referred to as its degree of "override." The aortic root can be displaced toward the front (anteriorly) or directly above the septal defect, but it is always abnormally located to the right of the root of the pulmonary artery. The degree of override is quite variable, with 5-95% of the valve being connected to the right ventricle.

Primary four malformations:

C: ventricular septal defect (VSD)◦A hole between the two bottom

chambers (ventricles) of the heart. The defect is centered around the most superior aspect of the ventricular septum (the outlet septum), and in the majority of cases is single and large. In some cases thickening of the septum (septal hypertrophy) can narrow the margins of the defect.

Primary four malformations:

D: Right ventricular hypertrophy◦The right ventricle is more muscular than

normal, causing a characteristic boot-shaped (coeur-en-sabot) appearance as seen by chest X-ray. Due to the misarrangement of the external ventricular septum, the right ventricular wall increases in size to deal with the increased obstruction to the right outflow tract. This feature is now generally agreed to be a secondary anomaly, as the level of hypertrophy generally increases with age.

Other Anomalies: There is anatomic variation between the hearts of

individuals with tetralogy of Fallot. Primarily, the degree of right ventricular outflow tract obstruction varies between patients and generally determines clinical symptoms and disease progression.

In addition, tetralogy of Fallot may present with other anatomical anomalies, including:◦ stenosis of the left pulmonary artery, in 40% of patients◦ a bicuspid pulmonary valve, in 40% of patients◦ right-sided aortic arch, in 25% of patients◦ coronary artery anomalies, in 10% of patients◦ a foramen ovale or atrial septal defect, in which case the

syndrome is sometimes called a pentalogy of Fallot◦ an atrioventricular septal defect◦ partially or totally anomalous pulmonary venous return◦ forked ribs and scoliosis

Tetralogy of Fallot with pulmonary atresia (pseudotruncus arteriosus) is a severe variant in which there is complete obstruction (atresia) of the right ventricular outflow tract, causing an absence of the pulmonary trunk during embryonic development. In these individuals, blood shunts completely from the right ventricle to the left where it is pumped only through the aorta. The lungs are perfused via extensive collaterals from the systemic arteries, and sometimes also via the ductus arteriosus.

Causes: Tetralogy of Fallot occurs in approximately 400 per million

live births. Its cause is thought to be due to environmental or genetic

factors or a combination. It is associated with chromosome 22 deletions and diGeorge syndrome.

Specific genetic associations include:◦ JAG1◦ NKX2-5◦ ZFPM2◦ VEGF

It occurs slightly more often in males than in females. Embryology studies show that it is a result of anterior

malalignment of the conal septum, resulting in the clinical combination of a VSD, pulmonary stenosis, and an overriding aorta. Right ventricular hypertrophy results from this combination, which causes resistance to blood flow from the right ventricle.

Pathophysiology: Tetralogy of Fallot results in low oxygenation of blood due to the

mixing of oxygenated and deoxygenated blood in the left ventricle via the VSD and preferential flow of the mixed blood from both ventricles through the aorta because of the obstruction to flow through the pulmonary valve.

This is known as a right-to-left shunt. The primary symptom is low blood oxygen saturation with or without cyanosis from birth or developing in the first year of life.

If the baby is not cyanotic then it is sometimes referred to as a "pink tet".

Children with tetralogy of Fallot may develop "tet spells". The precise mechanism of these episodes is in doubt, but presumably results from a transient increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the body.

Tet spells are characterized by a sudden, marked increase in cyanosis followed by syncope, and may result in hypoxic brain injury and death. Older children will often squat during a tet spell, which cuts off circulation to the legs and therefore improves blood flow to the brain and vital organs.

Blood flow in TOF

Signs and Symptoms:symptoms include a:

◦heart murmur which may range from almost imperceptible to very loud,

◦difficulty in feeding◦failure to gain weight◦retarded growth and physical

development◦dyspnea on exertion◦clubbing of the fingers and toes◦and polycythemia.

Diagnosis:The abnormal "coeur-en-sabot" (boot-

like) appearance of a heart with tetralogy of Fallot is easily visible via chest x-ray, and before more sophisticated techniques became available, this was the definitive method of diagnosis. Congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally.

Treatment:Emergency management of tet spells

◦ Prior to corrective surgery, children with tetralogy of Fallot may be prone to consequential acute hypoxia (tet spells), characterized by sudden cyanosis and syncope.

◦ These may be treated with beta-blockers such as propranolol, but acute episodes may require rapid intervention with morphine to reduce ventilatory drive and a vasopressor such as epinephrine, phenylephrine, or norepinephrine to increase blood pressure.

◦ Oxygen is ineffective in treating hypoxic spells because the underlying problem is lack of blood flow through the lungs and not oxygenation within the lungs.

◦ There are also simple procedures such as squatting in the knee-chest position which increases aortic wave reflection, increasing pressure on the left side of the heart, decreasing the right to left shunt thus decreasing the amount of deoxygenated blood entering the systemic circulation.

Treatment:Surgical: The Blalock-Taussig shunt (also referred to as a Blalock-Thomas-

Taussig shunt) is a surgical procedure to give palliation to cyanotic heart defects which are common causes of blue baby syndrome. In modern surgery, this procedure is temporarily used to direct blood flow to the lungs and relieve cyanosis while the infant is waiting for corrective or palliative surgery.

One branch of the subclavian artery or carotid artery is separated and connected with the pulmonary artery. The lung receives more blood with low oxygenation from the body. The first area of application was tetralogy of Fallot.

The procedure is no longer in use in its original form. Now a length of artificial tubing, 3 to 4 millimeters in diameter, is sewn between either the subclavian or the carotid artery and the corresponding side branch of the pulmonary artery, thus obviating the need to cut off blood supply and making it easier to regulate the blood flow to the lungs. Some centers now use a shunt directly from the right ventricle to the pulmonary artery, a Sano shunt. This is done to avoid the reduced diastolic blood flow in the coronary circulation associated with the Blalock-Taussig shunt.

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